From: Scott, Tyson C (tyson.scott@hp.com)
Date: Thu Mar 25 2004 - 13:17:14 GMT-3
If you have ip ospf demand-circuit on the router with the primary link
down once the idle time expires the circuit will go down. The routes
are set to DO NOT AGE so you will not truly remain up.
Regards,
Tyson Scott
Agilent Problem Management Team
Managed Network Services
Phone: 313-583-5812
Pager: 877-997-0811
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Packet Man
Sent: Thursday, March 25, 2004 11:02 AM
To: jphillips@ufcwdrugtrust.org; ccielab@groupstudy.com
Subject: RE: OSPF Demand circuit and Backup
Hey Joseph,
I see what you're saying but once the primary link goes down, doesn't
that
trigger ospf to flood lsa's out all it's interfaces so that all routers
can
sync their lsa databases?
And, once all lsa databases are in sync, don't all routers then know
that
the former primary link isn't available and therefore when the spf
process
is run, any paths that previously used the primary link will now use the
ISDN link instead?
And, if that's true, doesn't that mean that Dialer Watch isn't needed?
Or,
put another way, wouldn't configuring Dialer Watch, in addtion to OSPF
demand circuit be reduntant?
If this isn't true, can you describe a scenario where both Dialer Watch
and
OSPF demand circuit over the same isdn link would be needed?
Thanks, pm
>From: "Joseph D. Phillips" <jphillips@ufcwdrugtrust.org>
>Reply-To: "Joseph D. Phillips" <jphillips@ufcwdrugtrust.org>
>To: "Group Study (E-mail)" <ccielab@groupstudy.com>
>Subject: OSPF Demand circuit and Backup
>Date: Thu, 25 Mar 2004 07:44:06 -0800
>
>Dialer watch and OSPF demand-circuit accomplish two different purposes.
>
>OSPF demand only keeps the BRI link from flapping after the BRI's IP
>network is defined under the OSPF router process.
>
>By itself, it does not provide any reachability to any networks.
>
>If you want a true backup of a frame-relay network, you'd need
>dialer-watch, and you'd have to create a dialer map statement for each
>network which would be lost if the primary connection goes down.
>
>
>-----Original Message-----
>From: Packet Man [mailto:ccie2b@hotmail.com]
>Sent: Thursday, March 25, 2004 07:12
>To: ccielab@groupstudy.com
>Subject: OSPF Demand circuit and Backup
>
>
>Hi all,
>
>When an ISDN circuit is configured as an OSPF demand-circuit to backup
>another OSPF link in the same area, should and can any other backup
method
>such as Dialer Watch also be configured on the same ISDN link?
>
>My sense is that there's no need to configure any other backup method
and
>doing so would only complicate things and lead to unexpected results.
>
>Here's what I believes happens in such a situation (without 2nd method
>configured).
>
>Primary link goes down.
>
>This causes ospf to see a topology change has occurred.
>
>OSPF floods lsa over all links including ISDN circuit which brings up
ISDN
>circuit.
>
>OSPF updates the route table to reflect new topology.
>
>Now, user traffic that would have used the primary link now uses the
ISDN
>link.
>
>Is this simplified chain of events correct? Are there other
significant
>things that occur that we should be aware of?
>
>Thanks in advance, pm
>
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